Key Facts
- Duration
- Over 5 years (1939–1945)
- Merchant ships sunk
- 3,500
- Allied warships sunk
- 175
- U-boats lost
- 783
- German surface warships sunk
- 47
- UK weekly import requirement
- Over 1 million tons
Strategic Narrative Overview
The campaign peaked from mid-1940 to late 1943, with German U-boats operating in wolf packs against convoys crossing from North America to Britain and the Soviet Union. The Royal Navy, Royal Canadian Navy, and eventually the U.S. Navy provided escorts, while air power and improved technology such as radar and signals intelligence gradually shifted the balance. Allied forces overcame German surface raiders by end of 1942 and largely defeated the U-boat threat by mid-1943.
01 / The Origins
Britain, an island nation dependent on over a million tons of imported goods per week, faced strangulation if Atlantic supply lines were cut. The Allied naval blockade of Germany was announced the day after war was declared in September 1939, and Germany responded with a counterblockade using U-boats and surface raiders to destroy merchant shipping. Italy's entry into the war in June 1940 added Regia Marina submarines to the Axis effort.
03 / The Outcome
Germany's tonnage war ultimately failed as Allied shipbuilding outpaced losses and anti-submarine capabilities improved. The defeat of the U-boat threat cleared the way for the Allied buildup that made the invasion of occupied Europe possible. U-boat losses continued until Germany's surrender in May 1945, but the strategic victory belonged to the Allies, who kept Britain supplied and fighting throughout the war.
Belligerents & Mobilization Analysis
Side A
2 belligerents
Side B
4 belligerents